def is_prime(n):
    """
    to check if a number is prime or not.
    """
    if n <= 1:
        return False
    if n <= 3:
        return True
    if n % 2 == 0 or n % 3 == 0:
        return False
    i = 5
    while i * i <= n:
        if n % i == 0 or n % (i + 2) == 0:
            return False
        i += 6
    return True


def add_modify(a,b):
    """
    to add two numbers and modify the first number by adding the second number.
    """
    a += b
    return a


